| 摘要 |
<p>PURPOSE:To enable high sensitivity detection without affecting others by disconnecting the earth at one end of shield of a cable and constantly sending electric current with a frequency for an oscillator except the commercial frequency. CONSTITUTION:In a cable core wire 1 under the ground 6, electric current with commercial frequency is flowing. An oscillator 2 is connected in between one end of the outside shield wire 3 and the earth 4, and electric current is sent toward the earth 5. Since the current from the oscillator 2 thus flows through the shield 3, its magnetic flux is detected by a coil 7 on the ground. The magnitude of the magnetic flux is indicated by a wave detector 8, and so the position of the cable is known from this. The oscillator 2 must have a different frequency from the commercial frequency so that it can be easily distinguished from other noise by modulation. The wave detector 8 uses a filter to amplify only the frequency of the oscillator 2 so that it detects the modulation wave distinguishing the magnetic flux due to the current from the oscillator 2 from the other various magnetic flux.</p> |
